bdelloid rotifers evolution

[jozersky]

These asexual invertebrates are at least half a billion years old. How do they evolve? If they are reproducing asexually, shouldn't there be trillions of "species"? Every individual has the same genes, so every individual lineage should have its own special adaptions. Or are we those adaptions? I'm very confused.

Josh Ozersky
Brooklyn, NY

p.s. I just signed onto this board and have several questions about selection pressure that I've had for years. Is this the right place to ask them? Thanks!

[mith]

Some will die. If they are not sufficiently different from each other they are not considered a separate species.

[jozersky]

species are defined as organisms which can reproduce together. Asexuals can't be species by that definition....your answer isn't clear to me.

Josh

[Raegan]

basically asexual reproduction is cloning. the daughters are exactly the same as the mothers. that is not to say that evolution won't occur... it'll just be at a snails pace compared to the sexual reproducers.
during the process of cell division, mutations can occur. these can be silent, detrimental, or advantageous. these changes will be passed on to the daughters, who will pass it on, etc etc. over time, these changes will add up, and then you'll see the 'evolution'. every lineage will have it's own quirks. this does not make it a seperate species, just a different lineage from the same species.

[RobJim]

The word "species" doesn't apply well to asexually reproducing animals.

However, most authors, but especially Dobzhansky and Mayr, deny asexual organisms taxonomic membership in a species, because they are lacking in the one defining feature of a species as they construe them - interbreeding. Every individual in a clonal lineage is either genetically (and so phenotypically) identical to its parent or is a separate individual lineage. Each new mutation is not only a new variant but a whole new strain, and may be classified with its own binomial.

http://members.dodo.com.au/~wilkinsjandp/papers/metataxo.htm

Asexual organisms evolve by mutating. Once a mutation occurs, it cannot be shared with other 'sister' organisms, which is what sexual reproduction adds to the mix. Sexual reproduction allows for situations where two very similar organisms independently mutate advantageous traits, and can then combine these traits in offspring.

For an asexual organism to get two beneficial traits, it has to evolve one, and then some descendents of that animal must evolve the next one. For sexual reproducing species, an organism can develop one trait, and then any one of the millions of sister organisms can evolve the other, and then when the two lines mate, the superior organism with both traits exists. The latter method works better, clearly, but asexual organisms can still evolve.

[biostudent84]

Asexual organisms evolve by mutating. Once a mutation occurs, it cannot be shared with other 'sister' organisms, which is what sexual reproduction adds to the mix.

There are exceptions.

In some asexual organisms, like Spirilla, two members of a population will come together to share and exchange genetic material. This is not reproduction, as it is only the sharing of genetic material, not recreation.

[mith]

Righto, actually almost all bacterial species share genetic material. I remember in my bio book about 2 strains of bacteria that were injected into mice. One strain was lethal and one was benign. When dead lethal bacteria was injected along with living non lethal bacteria, the benign bacteria exchanged DNA with the dead and caused the mice to die.

[thank.darwin]

p.s. I just signed onto this board and have several questions about selection pressure that I've had for years. Is this the right place to ask them? Thanks!

Ask anything and everything!

[RobJim]

There are exceptions.

In some asexual organisms, like Spirilla, two members of a population will come together to share and exchange genetic material. This is not reproduction, as it is only the sharing of genetic material, not recreation

Good point, except that I don't think reproduction is necessarily recreational in most animals!